When manufacturing a liquid crystal display device, which is one type of a micro device, an exposure apparatus is used to project and expose a pattern of a mask (reticle, photomask, etc.) onto a plate (glass plate, semiconductor wafer, etc.), to which a photoresist is applied, with a projection optical system.
In the prior art, a step-and-repeat type projection exposure apparatus (stepper) is often used to perform batch exposure to transfer the pattern of a mask onto each shot region of a plate. Recently, a step-and-scan type projection exposure apparatus that has been proposed includes a plurality of small projection optical units arranged in plural columns at predetermined intervals in the scanning direction. The exposure apparatus continuously exposure-transfers the pattern of each mask onto each projection optical unit while synchronously scanning the mask stage and the plate stage (see e.g., Japanese Laid-Open Patent Publication No. 7-57986).
The enlargement of liquid crystal display devices has resulted in the enlargement of plates. Presently, plates (glass substrates) having a size of one meter square or more are being used. At the same time, masks have also become larger. As long as the exposure apparatus is required to have a constant pattern rule for devices, a large mask must have a thickness that is much greater than that of a small mask in order to suppress deflection and undulation of the large mask to an extent that is about the same as a small mask. A mask typically used for a TFT (Thin Film Transistor) is formed from costly quartz glass. Thus, a larger mask increases the manufacturing cost. This also increase costs such as the cost for maintaining the flatness of the mask and the cost resulting from longer inspection times for mask patterns.
A mask-less exposure apparatus, which exposure-transfers a pattern onto a substrate using a DMD (Digital Micromirror Device or Deformable Micromirror Device) in lieu of a mask, has been proposed. A DMD includes a plurality of micro movable mirrors (micromirrors) arranged in a two-dimensional array, with each micromirror a mirror surface being inclinable by ±12 degrees about a torsion axis. An electrode is arranged at the lower part of the mirror surface and driven to produce the two states of ON (+12 degrees) and OFF (−12 degrees). When the mirror is ON, light from a light source is reflected toward a projection optical system. When the mirror is OFF, the light is reflected into an absorbing body so that light is not projected outside. The mirrors are individually driven to function as a variable shaped mask that forms any pattern.
The states of a movable mirror may be divided into an operation time (the time during which the mirror changes its inclination+settling time) and a stable time (the time during which the position of the mirror is determined and stabilized). The operation time is an unstable state in which the mirror is changing its inclination or vibrating, and the position of the reflected light is thereby not stable. Thus, the reflected light, of which beam position is stable, can only be used during the stable time. That is, the reflected light does not contribute to exposure during the operation time. This lowers the illuminance in a scan type direct drawing exposure apparatus. When using a light source that emits a continuous light, the emission during the operation time is wasted. In order to ensure the energy required for drawing, a large output laser must be used or the scanning speed must be lowered to extend the stable time. However, this would increase costs and lower the throughput.